1. Field of the Invention
The present invention relates to a matrix-addressed display device to display one color by combining a plurality of basic colors, for example, R (Red), G (Green) and B (Blue), and its driving method.
2. Description of the Related Art
A liquid crystal display device capable of performing the color display by making use of a display element such as liquid crystal, and combining the light source and a color filter therewith, has been known. A thin film transistor addressing type liquid crystal display device is described below as an example, in which a picture element to perform one color display is constituted by combining three basic colors of R, G and B as the color filter, a large number of the picture elements are arranged in the display region, the signal line and the scanning line are arranged in the matrix to drive the liquid crystal and the pixel electrode is arranged in the region demarcated by the signal line and the scanning line, switching to the pixel electrode is performed by the thin film transistor and the electric field is applied to the liquid crystal corresponding to each pixel, the transmittance ratio of the liquid crystal is changed to switch the display/non-display.
In the display device for a computer to which such a liquid crystal display device is applied, the number of picture elements (one picture element is constituted by one set of R, G and B pixel) which are the unit of display is 640.times.480=307200 picture elements in the display of VGA specification to display 640 (transverse).times.480 (longitudinal) picture elements, and the number of the scanning lines and the signal lines are 480 and 1920 (=640.times.3) respectively because of three divisions into RGB along the scanning line. Thus, the total number of pixels is 640.times.3.times.480=921600.
FIG. 17 is a view illustrating a color liquid crystal addressing unit in which the addressing LSI is mounted on the screen of this type of color liquid crystal display device. In this figure, 1 denotes the liquid crystal display device in which the liquid crystal is filled between two transparent substrates which are arranged opposite to each other, one transparent substrate is provided with a common electrode and a color filter, and a large number of signal lines and scanning lines are arranged in the matrix in the longitudinal direction and in the transverse direction respectively on the other transparent substrate, and the pixel electrode and the thin film transistor are provided in the region which is surrounded and demarcated by the signal lines and the scanning lines, and in this example, a plurality of gate drivers Gd for addressing the scanning line are mounted on the left side part of the liquid crystal display device 1, and a plurality of source drivers Sd for addressing the signal line are mounted on the upper side and the lower side of the liquid crystal display device.
FIG. 18 is a partially enlarged view of the circuit of the liquid crystal display device 1 in this example, and in the circuit of this example, the signal lines S.sub.1, S.sub.2, S.sub.3 and S.sub.4 in the longitudinal row and the scanning lines G.sub.1,G.sub.2 in the transverse row are formed in a large number of matrixes in a crossing manner, a pixel electrode 5 and a thin film transistor 6 are provided in each region demarcated by the signal lines and the scanning lines, one region forming the pixel electrode 5 forms one pixel, and three pixels are collected to form one picture element.
Thus, in the circuit illustrated in FIG. 18, the picture element 7 surrounded by the chain dot line in FIG. 18 is constituted, and in the display device of the above-mentioned VGA specification, 307200 picture elements 7 are formed on one screen.
The source driver Sd and the gate driver Gd provided on the liquid crystal display device 1 of this number of pixels usually comprise one LSI having about 240 output pins, and the source driver and the gate driver to be mounted on the transparent substrate of the liquid crystal display device 1 are normally of TCP (Tape Carrier Package) type in which the LSI mounted on a polyimide tape is used, or of the COG (Chip On Glass) type in which the LSI is directly mounted.
So as to be adapted to 1920 signal lines and 480 scanning lines to be used in the above-mentioned display device 1, it has been necessary to use eight source drivers Sd having 240 pins (240.times.8=1920) and two gate drivers Gd having 240 pins (240.times.2=480) as illustrated in FIG. 17. In an actual liquid crystal display device, a separate circuit to feed the signal, etc., to the drivers is necessary but the explanation is omitted here.
As for the power consumption of the above-mentioned drivers, the power consumption of the source driver Sd is larger than that of the gate driver Gd as described below.
Power consumption of drivers: (about 840 mW)
* Gate driver: low (about 20 mW.times.2=40 mW: occupying 5%) PA1 * Source driver: high (about 100 mW.times.8=800 mW: occupying 95%)
It is also known that the source driver is generally about two times as expensive as the gate driver in the cost.
The power consumption of the above-mentioned source driver is for the typical 6 bit (gray scale number: 64) with color display in the present status, and in the case of the source driver of 8 bit type, both the price and the power consumption are increased, and the difference in the price and the power consumption between the gate driver and the source driver are further increased.
In the condition background, it is desired to reduce the required number of these expensive drivers in order to reduce the cost and the power consumption of the liquid crystal display device in which the size of the screen is further increased and the gray scale is promoted.
If degradation of the image quality such as flicker is generated in exchange for reduction of the power consumption, the degradation becomes remarkable because of the large size of the screen. Thus, it is necessary to reduce the power consumption and to maintain the image quality, and it is desired to efficiently drive the liquid crystal display device while these excellent characteristics are satisfied.
The present invention copes with the above-mentioned circumstances, and the purpose of the present invention is to arrange the picture element to display one color by combining a plurality of basic colors, to reduce the power consumption in the drive circuit system in the matrix-addressed display device, and to provide the liquid crystal display device not to cause degradation of the image quality and its driving method.